1. Technical Field
The present invention relates to electronic circuitry contrived so as to allow the passage of an incremental encoder's signal when such encoder is mechanically driven in a forward rotation. The circuitry is further contrived so as to maintain or latch the last encoder state to its output upon detection of reverse rotation of the encoder as a condition of its mechanical application. Further, the circuitry inhibits the re-establishment of the forward rotational signal transitions to its output until a equal displacement of forward rotation offsets the total displacement of reverse rotation discerned by the circuit and the instantaneous encoder input state matches the latched output of the circuit. Further, the circuitry is contrived so as to inhibit the passage of the encoder's index pulse while the circuit's output lines are latched to a constant state. Such circuitry finds practical application in the control or monitoring of mechanical apparatus such as a collator conveyor predisposed to mechanical reverse travel from its intended motion.
2. Background Art
An incremental encoder translates the rotational motion of its shaft into two output signals exhibiting a phase difference of nominally ninety degrees. The signals' phase difference results in a presentation of four output states to discriminating circuitry intended to process the resultant signal. By discriminating the sequence of the presented quadrature signal, relative forward or reverse rotation may be discerned. Forward and reverse rotation within the context of this invention is relative and may be arbitrarily defined. An incremental encoder may be further contrived so as to supply an index pulse output to discriminating circuitry annunciating a complete revolution of the encoder's shaft. An incremental encoder provides transitional signals to host controls assisting in the synthesis of positional data of the controlled mechanism enabling various control functions of the mechanism.
A characteristic of mechanical systems driven by electric motors and constrained by brakes against varying mechanical loads is the disposition toward reverse motion. The direction of useful production is referenced herein as forward rotation. Functional control of the system is assisted by positional data derived from the monitoring and accumulation of pulses emanating from an incremental encoder which is mechanically coupled to the system. Further, various devices augmenting the processing features of the system may require precise positional data as exemplified by an ink jet printer situated along a collating conveyor.
The final quality of the product produced by such a processing system depends upon the containment of the effects of reverse line motion often described in mechanical systems as backlash. Processing controls also utilize positional data derived from totalized incremental encoder signals to track the forward progress of a product situated along the processing system. Mechanical backlash, improperly compensated, acts to reduce the quality of ink jet applied images as well as contributes to a loss of positional control of the product along the processing system. Inaccuracies in product tracking, resulting from improper backlash compensation or no backlash compensation, contribute to ineffective device control along the course of a collating conveyor. Systems relying on the proper presentation of the index pulse for positional control may become faulty as a result of multiple index pulse transitions produced by a reciprocating angular motion of the encoder shaft.
Electronic circuits for compensating mechanical backlash encountered by an incremental encoder having quadrature and index outputs are known. For example, a type of filter circuit may be located between the incremental encoder and the control circuitry t inhibit the passage of reverse direction signal sequences. In such a manner, only forward transitions are passed to the control circuitry. The output of the filter circuit is a single phase pulse train signal derived from the input quadrature sourced by the incremental encoder. Since the incremental encoder provides a quadrature source signal comprised of two discrete signal lines and appropriately phased, and the filter circuit provides a single output line to the controller, the integrity of the quadrature output of the encoder is lost when a filter circuit is employed. Further, such filter circuitry does not preserve the proper sequencing of the index pulse for encoders so equipped.